1. Field of the Invention
The present invention relates to a grinding method to grind a workpiece of ferrous and/or non-ferrous metals, alloys containing at least one or more materials including these metals and/or others, with the use of a magnetic attraction system.
2. Description of the Prior Art
Although a machining process has rapidly been automated and a machining accuracy has also been greatly improved as a popularization of NC machine tools or the like goes on, grinding or polishing operations are still taking an important role in final finishing processes, which are at present almost always carried out by manual methods requiring much time and labor.
Analyzing these manual finishing-works from a viewpoint of performance, most are characterized by a monotonous pattern to repeat a rectilinear motion while pressing a grindstone on a surface to be ground and in general the rectilinear motion itself is relatively simple. Accordingly if the user attaches a grinding tool to an end of a robot arm and teaches such rectilinear motion to the robot and re-enacts it, an automatization of the grinding process will soon be possible to be realized. For instance, a "dead-weight" system is one of the so-contrived grinding methods, in which a grindstone loaded with a certain weight is fitted to an end of the robot arm which is actuated to X- and Y-directions of the coordinates.
In this "dead-weight" system, however, the whole weight of grinding tool itself becomes considerably heavier and also a moment of inertia affected on the arm becomes too large because a grinding pressure is produced by a loaded weight. Consequently it is impossible to move the grindstone rapidly and stably on the surface to be ground and in the worst case it may happen that the grindstone leaps up or rebound from the surface to be ground. This inevitably results in a deterioration of the grinding performance. Also, since a spring force system will be most likely formed in a pressing means of the grindstone as a result of the employment of a weight, the frictional vibration at the time of grinding becomes larger because it is superposed upon a natural vibration of the arm. In addition to the above, there may be some cases where several laterally-striped patterns are created perpendicularly against a grinding direction along the surface to be ground and in consequence an optional grind surface is hard to be obtained.
Also, in actual cases there are many varieties in the shape of workpiece surfaces, e.g., as typified in dies or the like, in which not only a simple straight-surface but also a complex curved-surface or a combined pattern thereof are included, and their patterns are often formed not merely on a plane surface but on a side or cavity surface.
If the surface to be ground comprises such a complicated pattern, the grinding motion will inevitably be affected by gravity of the weight load. As a result, it becomes impossible to do grinding of a side surface and also a profiling of a free curved surface. Especially, there will be such cases where a proper grind can not be attained because a grinding pressure is affected by an inclination of the surface to be ground and in consequence can not be loaded evenly on the workpiece surface.